The Influence of the Rate of Deformation on the Strength of Materials in Tension

There is growing significance to the tension impact test in comparing the usefulness of materials for service conditions in which dynamic loading occurs. Many recent investigations have begun the study of the dynamic properties of materials, and have attempted to correlate. their results with the existing theories of strength of materials. Few investigators have succeeded in developing their experimental procedure in impact testing to the point of determining basic tensile properties measured by the stress-strain diagram. This thesis discusses a method of determining stress-strain relations for materials under tension impact loads at various speeds. Tension characteristics of eight different engineering alloys are discussed for rates of deformation from 10 to 190 feet per second. Comparison with results from static tests is made for these materials, and the influence of the rate of deformation is noted. The results indicate that in general, for the materials tested, the yield and ultimate stresses under dynamic conditions are higher than for static conditions; and quantitative data are tabulated as a function of the rate of deformation. The dynamic energies absorbed in tension impact are usually larger than the static values, but they may decrease in the case of certain heat treated steels. Results do not indicate a critical velocity of embrittlement for any of the materials tested within the range of velocities reported. Use of any single type of geometrical deformation of the material as a measure of the resistance of the material to dynamic loads is not found possible. Application of this test procedure is suggested as a basis for investigating the relative usefulness of different heat treatments and alloying of metals for service conditions involving dynamic tensile loading.